Laser direct imaging for the printed circuit board industry is an emerging manufacturing technology which promises fast turn-around, high yield and the precision required for future generations of high density, fine line printed circuit boards. The need to mass-produce microscopically dimensioned, etched configurations has resulted in demand for resists with the properties of greater speed and improved image resolution and processing integrity to reduce the unit cost of the end-product board. "Speed" as used herein refers to the sensitivity of the composition to activating radiation and is not to be confused with development rates.
Photoresists have been developed for laser direct imaging based on the mechanism of light-induced imagewise hardening of a polymer coating. However, light-induced hardening of a polymer coating generally is a low speed process. Furthermore, the hardening mechanism is usually based on the photopolymerization of a monomer system which is subject to swelling in the development process. Consequently, the final resist image tends to exhibit poor resolution and integrity.
Thus, the problem solved by this invention is to provide a negative-working photoresist composition, suitable for laser exposure direct imaging, that is capable of higher speed than prior art resist compositions and which exhibits improved image resolution and processing integrity.